Centering means for cathode-ray deflecting circuits



Patented Nov. 8, 15949 CENTERING MEANS FOR CATHODE-RAY DEELECTING CIRCUITS Paul F. G. Holst and Loren Robert Kirkwood,

Oaklyn,

N. J., aSsignor to` Radio Corporation of America, a corporation of Delaware Application October 28, 1944, Serial No. 560,755

3 Claims.

The present invention relates to cathode ray tube circuits, and more particularly to a novel centering means for placing the trace in the desired location on a cathode ray indicator or image producing tube or the like.

The principal object of the present invention is to provide a novel and suitable centering means which maintains optimum focusing o the cathode ray tube over the entire range of adjustment provided by the circuit.

Another object of the invention is to provide a novel and reliable source of centering voltages which is of the balanced push-pull type and thus maintains the best focus condition regardless of the setting of the centering control.

Still another object of the invention is to provide a simple balanced push-pull centering means which can be produced from standard, commercially available, component parts.

Other objects and advantages of the invention will, of course, become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specilicaticn in connection with the accompanying drawing which shows, illustratively and schematically, a cathode ray indicator circuit embodying the invention.

Referring to the drawing, a cathode ray tube lll of the usual type is shown as being connected to external circuits in such a manner that separate alternating deflection voltages applied to deflection voltage input connections or terminals |2` and lil will produce a trace or pattern on the iluorescent screen l@ of the tube.

Electrostatic deectio-n plates I1 and |8 deflect the electron beam lil developed within the tube in one plane, while electrostatic deflection plates 2|; and 2:2 dellect the beam in a plane at right angles to the direction controlled by the plates l1 and I8. The resultant deflection of the beam I9, as the voltages applied to the input connections l2 and Ul vary, causes the beam as it impacts upon a target area, such as the usual fluorescent or luminescent screen i5, to traceV a distinctive visual raster or pattern. The electron beam lil is produced in a well-known manner by an electron gun comprising an electron source in the form of an indirectly heated cathode 2li, a control electrode or grid 25, and an electrode 21 which functions as an accelerating electrode. ThisI electrode 21 is usually referred to as the second anode and in some instances is a cylinder or is in the form of a coating on the envelope or wall of the tube. The resulting luminous spot on the cathodez ray screen lli can, in lrnown'manner, be reg.- 55

i 21 to the voltage on the anode 28.

ulated as to size and intensity by suitable choice ofV electrode voltages. An additional anode 28, normally referred to as the rst anode, cooperates with the anode 21 in varying the spot size and intensity. These electrodes are of usual and known construction. To this end, the electrode 28 may be connected to a variable potential source in known manner which may be adjusted to the correct value with respect to that applied to the electrode 21. The voltage applied to the second anode 21 and its relationship to the centering voltages for a pair of deflecting plates, for example plates |1 and I8., will be discussed more in detail hereinafter as it constitutes a part of the present invention. Likewise, the control grid 26 is connected in known manner to a potential source which is negative with respect to the cathode and is preferably made adjustable.

Suitable direct current sources, for example rectiers (not shown) are connected to terminals 29', 3|, and 32. Suitable voltages may be obtained from the sections 33, 34, 65, 65, 51, and 68 of bleeder resistor circuits connected between the terminals 2-9, 3|, and 32. The negative terminal 3| may be grounded, or with slight circuit modifications, which are Well known to those skilled in the art, the positive terminal 32 or some intermediate potential, as shown, may be grounded so as to place the cathode 24 and the heater 35 at a high negative potential with respect to ground whereby conducting portions in the apparatusv presenting dangerous voltages can more easily be made inaccessible. Cathode potential is provided at the junction of 61 and 68, while a variable D. C. voltage negative withv respect to the cathode 24 for' the grid 26 is provided at the movable arm of 68. The anode 28; is also provided with a variable potential, positive with respect to the cathode 24 from the arm 4|! of B5. These variable voltages are supplied to the cathode ray tube at the arms 39 and 40; respectively.

Focusing of the lluorescent spot produced by the beam I9` is controlled in the usual manner by adjustment of the ratio of the voltage on anode This may be done conveniently by varying the magnitude of the voltage applied to the arm 4E).

Regulation of the spot size and spot intensity can be accomplished byvarying the current to or voltage on the anode 21. The current to the anode' 21 may be increased by decreasing the bias voltage applied to the grid 26. An increase in the anode current of the anode 21 increases the size and intensity of the spot. An increase in the voltage applied to theV anode '21 increases the speed of the electrons which increases the spot intensity and may decrease the spot size. It will be understood, therefore, that the grid 26 may be reserved for modulating the beam I9 if the tube I is to be used for production of television images or the like.

The deflecting voltages applied to the previously mentioned sets of terminals I2 and I4 may be amplified or otherwise modied, if desirable or necessary, in circuits 42 and 43. The circuits 42 and 43 may also include deflection generators, such as oscillators for producing a desired wave form, or other deflection circuits. The connections |2 and |4 may then be omitted or used only to apply control pulses. The deilecting plates and I8 are connected to the output of the amplifier 42, if desired, through coupling condensers 46 and 41. Likewise, the plates 2| and 22 are connected to the output of the circuit 43 by condensers 48 and 49. It will be understood that each of the circuits 42 or 43 may comprise any suitable or special coupling network or mesh which is to be interposed between the terminals I2 and the plates and I8, or the terminals I4 and the plates 2| and 22. In the arrangement shown for the purpose of illustrating the invention, the circuits 42 and 43 may be of the balanced push-pull type, although one or both may be unbalanced and single ended.

The deecting plates 2| and 22 are connected in push-pull to the circuit 43 through coupling capacitors 48 and 49, while centering voltages are supplied through resistors 5I and 53 from a centering network. This circuit may be similar to that disclosed and claimed in the application of the present inventors, Serial No. 560,756, entitled Centering means for cathode-ray deflecting circuits, issued December 7, 1948, as Patent 2,455,771, led concurrently herewith. This network comprises resistors 56, 69, 55, and 52. However, if desirable, other centering circuits may be used on these electrodes.

The plates Il and I8, in accordance with the invention, are connected to a voltage divider comprising resistors 60, 6I, and 62. Resistor 6| is adjustable as shown from its maximum value to a setting of the adjusting means i3 that shunts out this resistor. The plates and I8 are connected as shown effectively at each end of the adjustable resistor 6|. The resistors 60 and 62 are preferably substantially equal in resistance value, whereas the maximum resistance value of the resistor 6| is considerably higher that that of either 60 or 62. Solely by way of example, the resistor 6| may have a maximum value of one megohm, and the resistors 69 and 62 may have a value of 150,000 ohms each.

The amplifier 42 is labeled as a sweep amplier by way of example, and therefore plates and I8 serve for what are normally known as the horizontal delecting plates whether the invention is applied to an indicator as stated above, the image producing tube of a television system, or for other purposes. A voltage is produced on the deiiection plate which varies with the setting of the centering control adjustment means 13 from a value equal to one-half of the voltage applied between the terminals 29 and 32 when the resistor 6| is shorted out by the adjustment means 'I3 to a value approximately equal to one-tenth of the total voltage with the entire resistor 6| in circuit. The voltage on the deection plate I8 varies from one-half of the voltage appearing across the terminals 29 and 32 when the entire resistor 6| isvshorted to approximately nine-tenths of the total voltage when the resistor 6I is in circuit. These two voltages on the deection plates I? and IS always have an average voltage on them of one-half of the value of the voltage applied across the terminals 29 and 32.

Since, for the particular wave forms used, it may be required that the centering voltage for this sweep deflect the beam so that the spot is normally on the right-hand side of the tube, then, if the deecting plate I8 is on the right side, the sweep may be centered using this circuit.

To obtain the best focus conditions for a cathode ray tube, such as the tube I0 shown illustratively, the average voltage on the deflection plates I'l and I8 should equal the voltage on the second anode 2l. As was pointed out above, the average voltage on the deflection plates is always equal to, or approximately equal to, onehalf of the voltage impressed across the terminals 29 and 32. Using the centering circuit disclosed for the plates I'| and I8, this condition will be realized if the second anode bleeder, comprising the resistors 33 and 34, is so designed that the voltage on the second anode 21 is equal to onehalf of the voltage impressed across the terminals 29 and 32 or the average voltage on the deflecting plates.

Various modications of the invention shown and described herein by way of example are possible without departing from the spirit and scope of the invention described herein, and it is desired that any and all of such modications be considered within the purview of the present invention defined by the hereinafter appended claims.

Having now described the invention, what is claimed and desired to be secured by Letters Patent is the following:

1. Cathode ray tube apparatus comprising a cathode ray tube having means to produce a cathode ray beam and being of the type employing electrostatic focusing of the cathode ray beam, said tube having cooperating focusing electrodes, one of said electrodes having a substantially xed voltage applied thereto, a pair of delecting plates for deecting said beam, and a centering control for said beam comprising means to apply variable voltages to each plate of said pair, said means acting to maintain a substantially constant ratio between the average of the voltages on said pair of plates and said substantially xed voltage applied to said electrodes.

2. Cathode ray tube apparatus comprising a cathode ray tube having means to produce a cathode ray beam and being of the type employing electrostatic focusing of the cathode ray beam, said tube having cooperating focusing electrodes, one of said electrodes having a substantially fixed voltage applied thereto, a pair of deflecting plates for deflecting said beam, and a centering control for said beam comprising a variable resistor to apply variable voltages to each plate of said pair, said resistor acting to maintain a substantially constant ratio between the average of the voltages on said pair of plates and said substantially iixed voltage applied to said electrodes.

3. Cathode ray tube apparatus comprising a cathode ray tube having means to produce a cathode ray beamand being of the type employing electrostatic focusing of the cathode ray beam, said tube having cooperating :focusing electrodes, one of said electrodes having a substantially fixed voltage applied thereto, a pair of deecting plates for deflecting said beam, and a centering control for said beam comprising a Variable resistor to apply variable voltages to each plate of said pair, said variable resistor being connected at each of its ends to said plates to maintain a substantially constant ratio between the average of the voltages on said pair of plates and said substantially fixed voltage applied to said electrodes.

PAUL F. G. HOLST.

LOREN ROBERT KIRKWOOD.

, REFERENCES CITED UNITED STATES PATENTS Number 15 473,650 503,502

Name Date Knoll Mar. 15, 1938 Diehl et al. Apr. 4, 1939 Norman Apr. 11, 1939 Norton Nov. 21, 1939 Gloess Sept. 3, 1940 Sherman Sept. 1'7, 1940 Shepard, Jr Nov. 12, 1940 Rohats Jan. 6, 1942 Browne et al June 16, 1942 FOREIGN PATENTS Country Date Great Britain Apr. 15, 1935 Great Britain Oct. 6, 1937 

